Recently, by increased integration of integrated circuits, submicron pattern formation is required. Particularly, lithography using excimer laser from krypton fluoride (KrF) or argon fluoride (ArF) is paid to attention since it enables production of 64 M DRAM to 1 G DRAM. As the resist suitable for such excimer laser liphoraphy process, a so-called chemical amplification type resist utilizing an acid catalyst and a chemical amplification effect is being adopted. When a chemical amplification type resist is used, an acid generated from an acid generator at irradiated part is diffused in the subsequent heat treatment (post exposure bake: hereinafter, abbreviated as PEB in some cases), and the solubility of the irradiated part in an alkali developer is changed by a reaction using the resulted acid as a catalyst, thus, a positive or negative pattern is obtained.
For providing a chemical amplification type positive resist, particularly, a positive resist for KrF excimer laser lithography, a poly(hydroxystyrene)-based resin in which a part of phenolic hydroxyl groups is protected by a group dissociating by the action of an acid is often used in combination with an acid generator. As such a group dissociating by the action of an acid, those forming an acetal type bond with an oxygen atom derived from a phenolic hydroxyl group, for example, those having a structure in which tetrahydro-2-pyranyl, tetrahydro-2-furyl or 1-ethoxyethyl is bonded to an oxygen atom, are paid to attention, from the standpoints of resolution, sensitivity and the like. However, there is a limitation on resolution even if such a resin is used.
Further, in pattern formation by photolithography, in general, the finished size of a resist pattern tends to vary depending on variation of exposure amount, and exposure latitude (also called exposure margin) is small. Thus, in conventionally known resist compositions, resolution, sensitivity, exposure clearance and the like are limited. Further, for production of an integrated circuit, dry etching is conducted using a resist pattern formed by photolithography as a mask. Therefore, the resist used in this is required to have also heat resistance and dry etching resistance.
The object of the present invention is to provide a chemical amplification type positive resist composition excellent in various abilities such as sensitivity, resolution, heat resistance, film thickness after development at unexposed area, applicability, exposure clearance, dry etching resistance and the like, particularly, having further improved resolution and exposure clearance.
The present inventors have intensively studied for attaining such an object, and resultantly found that excellent abilities are obtained by using at least one hydroxystyrene-based copolymer selected from 3-hydroxy-1-adamantyl acrylate and 3,5-dihydroxy-1-adamantyl (meth)acrylate, as a resin component of a chemical amplification type positive resist, completing the present invention.